In recent years, many proteins related to silicon oxide have been discovered, and attempts are made to put the proteins to various uses (e.g., a technique of polymerizing silicon oxide, a technique of fixing a desired substance on silicon oxide, and a technique of purifying a desired substance fixed on silicon oxide).
For example, Patent Literature 1 discloses a particular protein (CotG protein) derived from Bacillus bacteria, and a polypeptide of a fragment of the protein. In the technique disclosed in Patent Literature 1, silica is polymerized with use of the protein and a fragment of the protein.
Patent Literature 2 discloses a particular protein (SBP: silica material binding protein) which is capable of binding to silicon oxide (e.g., silica), and a tag derived from the protein. In the technique disclosed in Patent Literature 2, a fusion protein of a tag and a desired protein is used so that the desired protein is fixed on silicon oxide via the tag.
Patent Literature 3 discloses a particular protein (SBP: silica material binding protein) which is capable of binding to silicon oxide (e.g., silica), and a tag derived from the protein. In the technique disclosed in Patent Literature 3, a fusion protein of a tag and a desired protein is used so that the desired protein is fixed on silicon oxide via the tag, and further with use of a divalent cation-containing solution, the desired protein is dissociated from the silicon oxide.
Patent Literature 4 discloses a peptide which is capable of binding to silicon dioxide. In the technique disclosed in Patent Literature 4, a fusion protein of a peptide and a desired protein is used so that the desired protein is fixed on silicon dioxide via the peptide, and further with use of an arginine-containing solution, the desired protein is dissociated from the silicon dioxide.
Note that in conventional techniques, in order to prevent a protein other than an intended fusion protein from being adsorbed nonspecifically on silicon oxide or silicon dioxide, the fusion protein is fixed on silicon oxide or silicon dioxide in a solution containing a salt in high concentration. Further, in the conventional techniques, the use of the solution containing the salt in high concentration enables purification of a high purity fusion protein.
As described above, attempts have been made to put proteins related to silicon oxide to various uses, among which the technique of purifying a desired substance fixed on silicon oxide is particularly attracting a great interest, and early development of the technique is hoped for. For the technique, it is important to discover not only a tag capable of binding to silicon oxide, but also a method for causing a tag which is bound to silicon oxide to be specifically dissociated from the silicon oxide.